Until around 1934, when a large number of new legislative
routes were added, trunk highways were virtually always numbered
the same as their constitutional or legislative route numbers. In
general, with the Constitutional Routes, lower numbered highways
were the more primary routes. Since that time, there is no real
pattern or hard and fast rule to numbering Minnesota routes.
Generally, the designation is based on one of the following
criteria:

It may be designated the same as its L.R.
number, or the L.R. number of one segment of a trunk
highway with several legislative route numbers;

It may have an arbitrarily assigned
number, usually less than 125;

It may be numbered based on association
with another highway (although 3-digit numbers generally
do not indicate such an association).

Note that I don't list "clustering" as a criterion
for numbering. Actually, there is some clustering of the legislative
route numbers, which occured as groups of highways were
authorized at the same time, and thus nearby routes received
adjacent legislative route numbers. In this instance,
geographically close highways might be numbered in a cluster if
their legislative and trunk highway numbers are the same. Between
the "arbitrary" route numbers and routes that match
their legislative/constitutional route numbers, all numbers 124
and less have been used at least once. Numbers used for U.S. or
interstate routes are not reused arbitrarily as state numbered
routes elsewhere. However, several state-numbered routes are
extensions of a U.S.-numbered route (61, 65, 169, and formerly
212), even though only one of these current state routes (169)
touches its parent U.S. route. This latter convention doesn't
really violate the no-duplication rule. There is one numbering
quirk: by taking this link to explore MN-62, you can find out why
there are two routes so numbered .

It should be noted that MnDOT hates to duplex U.S. with
Interstate routes. U.S. 52, which is duplexed with I-94 for 230
miles from North Dakota to St. Paul, is not marked at all along
the route (with the possible exception of a few old guide signs
that have not yet been revised). Even U.S. 12, which is duplexed
with I-94 for 25 miles between Minneapolis and Wisconsin, is not
marked either. Typical of the marking used to indicate the
co-numbered segment is a sign on U.S. 52 just prior to joining
I-94 that reads, "(U.S. 52) Follow (I-94) West." That's
the last you see of 52 until entering North Dakota. U.S. 61,
which used to be duplexed for 120 miles with I-35 between Wyoming
and Duluth, was decommissioned, and north of Duluth was
redesignated MN-61 to the Canadian border.

Major renumberings. The all-time major renumbering
occurred in 1934, when around 140 new legislative routes were
added at one time. This major addition of routes necessitated a
revamping of the numbering system, and the resulting network
looked much like today's. At the same time, there was a change in
U.S. highways. U.S. 55, 10S and 10N were eliminated, and U.S. 52
introduced. Shortly thereafter, in 1935, U.S. 63, 69 and 59 were
added to the system, which necessitated changing of state trunk
highways with those numbers. The 1934 map shows changes that
disappeared a year later, particularly in the length of newly
extended U.S. routes (65, 212, 218). According to old Department
of Highways documents, the markings shown on the 1934 map were
indeed posted that year, and then updated in 1935 to reflect the
approved U.S. route numberings. (My unsubstantiated guess is that
Minnesota jumped the gun on AASHO approval of the numberings and
had to back off the next year). A significant renumbering around
1963 consolidated and broke up route continuity along quite a few
routes as well.

Business routes. There are currently two trunk highways
marked as the business route of another trunk highway: U.S. 2
Business through East Grand Forks, and MN-371 Business through
Brainerd. However, there are other business routes in Minnesota,
most of which are under local or county control. There are
business loops of I-94 at Moorhead (old MN-231, but now a city
street); I-90 at Fairmont and Austin (on county and city roads,
respectively); and I-35 (following U.S. 65) at Albert Lea. There
is also a business route on and MN-23/U.S. 71 at Willmar (a city
street). This latter route is interesting for the signs used:
apparently made by MnDOT, they are a green cutout U.S. shield for
Business 71 and a green square for Business 23 (both read
"Business xx"). A more common convention is to maintain
a county route through a city on the former trunk highway route
and mark it with its county route number and the supplemental
legend "Thru City." A good example of this is the route
marked from U.S. 10 at Little Falls. The only trunk highway
marked this way is MN-197, old U.S. 2/71 through Bemidji, which
is marked "MN-197 Thru City."

Route Markers --- Past and
Present

There have been three general "eras" of route
markers since the 1920s, as illustrated below:

The original state route marker design used after
1920 was a yellow star in a black circle, on a square
yellow background. These markers were originally
stenciled on telephone poles and later put on signs. This
is a photograph of a sign in the collection of Robert
Edgar of Bakersfield, CA. When found, it had a white
background like the sign depicted below, but yellow paint
underneath. Thus, it may have originally been
posted along the original Trunk Highway 7 --- also U.S.
14 --- and then repainted and moved to the new T.H. 7
established in 1934. Robert did an excellent job
restoring the sign to its original colors.

In the major route renumbering of 1934,
the former yellow markers were replaced with white
background markers. This design was used until around
1954. Texas is the only other state to have used a star
design, and no North American entity uses this primary
design feature today. A possible reason for a design
change was that this design did not display three-digit
numbers adequately.

U.S. routes originally were the
traditional cutout, Minnesota/U.S. xx signage. These were
gradually replaced by the 1950s by other, transitory
styles that abandoned the cutout style and used either
"U.S." or "MINN" over the top line.
Some "MINNESOTA/U.S. " signs on a black
background were also used and were seen on the road into
the 1980s. This sign from the collection of Robert Edgar
(Bakersfield CA).

The next design introduced in the
mid-1950s, and used until the late 1960s, was similar to
today's Maryland route markers: all white background,
with the legend MINNESOTA in the top one-fourth , and
separated from the number portion of the sign by a line.
Effective at displaying all numbers, but as bland as
Swedish cooking.

U.S. signs went through several
alternative, non-cutout designs; I've chosen the one used
on state maps of the era. It may not be clear, but the
U.S. shield is on a white, square background. Other
designs used had "U.S." over the line or
"Minnesota/U.S. xx" on either a white or black
background.

Around 1968, the current state marker design was
introduced. It is distinctive among state route markers
for several reasons. First, it is the only sign in the
U.S. that uses a blue background. (Several Canadian
provinces use blue-background route markers on some of
their routes.) Second, like Tennessee's, it has the state
outline as a secondary, rather than as the primary design
element. Finally, it uses three colors (blue, yellow and
white) --- though when first introduced, the signs had
yellow numbers, and a few of these signs still exist.
That shade of yellow varies somewhat --- sometimes it's
the shade of Gulden's Mustard, sometimes it's reddish. I
think it's supposed to be gold. Virtually all three-digit
reassurance marker signs are square, using a compressed
font if necessary, but on guide signs rectangular
three-digit signs with standard width FHwA font are
standard.

The only U.S. marker used today is the
standard U.S. shield on black background, with no text.
Lacking a photo or a scanned image with a Minnesota U.S.
route number in it, I am using one of the graphics
created for my route listings as illustration. A
California cutout style with only "U S" over
the number was formerly used on freeways in conjunction
with Interstate markings, but now in the rare instances
U.S. routes are marked on interstates, the standard
design is used.